How hard is the water in Custer County, SD?
15.5 grains per gallon
A softener will pay its way here.
The median hardness measured in Custer County, SD is 265 mg/L as calcium carbonate, which is 15.5 gpg. That is very hard on the USGS scale. It comes from 164 samples at 81 sites between 1990 and 2021, drawn from groundwater wells, which is what most taps and private wells in the county draw on.
How much it varies here
Half the sites came in between 11.2 and 21.8 gpg. The whole middle of that range gives the same answer, so a test of your own tap is unlikely to change it. Confidence in the county figure: high (how it is measured).
What to do next
At 15.5 gpg a softener pays its way here. Before you buy, check the quoted unit's grain capacity against the sizing table below, and ask whether it regenerates on demand, which uses less salt than a timer. Call your utility for its own report if you are on city water.
More on sizing a softener for your household.
From 5.3 to 122.7 gpg
The softest single sample on record in Custer County was 91.3 mg/L and the hardest 2,100 mg/L, a 23-fold gap. The top quarter of sites read above 21.8 gpg and the bottom quarter below 11.2 gpg.
Wells 15.5 gpg, rivers and lakes 15.1 gpg
164 groundwater samples from 81 wells put the median at 265 mg/L. 247 surface samples from 26 sites put it at 257.8 mg/L. In Custer County the wells come out 0.4 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. The two sources are close, so the county figure should hold whichever one your tap is on.
What a softener would cost to run
For a household of 3, a 24,000-grain unit covers a week between regenerations. Expect about 338 lb of salt a year (9 bags of 40 lb, about $61), and roughly 2,346 gallons of regeneration water. Installed, most units run $1,000 to $4,500; spread over 15 years with salt, that is about $161 a year.
Sizing at 15.5 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 930 | 24,000 | 113 lb |
| 2 | 1,860 | 24,000 | 226 lb |
| 4 | 3,720 | 32,000 | 453 lb |
| 6 | 5,580 | 40,000 | 679 lb |
Custer County against the rest of South Dakota
Among the 55 South Dakota counties with data, Custer County is number 39 of 55 counting from the hardest. Across the whole country it is harder than 71% of counties.
Softest in South Dakota: Dewey County at 0.5 gpg. Hardest: Hanson County at 84.7 gpg. Closest to Custer County: Perkins County (15.1), Stanley County (16.1), Hughes County (16.4).